Cellulose nano-whisker, preparation method thereof, silanization modified cellulose nano-whisker and application of silanization modified cellulose nano-whisker

Abstract

The invention provides a cellulose nanowhisker, a preparation method of the cellulose nanowhisker, a silanization modified cellulose nanowhisker and application of the silanization modified cellulose nanowhisker, and belongs to the technical field of preparation of cellulose nanowhiskers. According to the method, the sodium hydroxide solution and the algae plant powder are mixed and then subjected to soda boiling treatment, lignin, hemicellulose and other impurities can be deeply removed, and therefore cellulose fibers with high purity are obtained. According to the method, the suspension obtained after soda boiling is mixed with the oxidizing agent solution, so that residual lignin after soda boiling can be removed, cellulose fibers can be bleached, and the purity of nanocellulose can be improved. According to the method disclosed by the invention, the acidic low cosolvent is utilized to enable the nanocellulose to be subjected to hydrolysis reaction, an amorphous region in the nanocellulose is attacked to hydrolyze the nanocellulose, and a highly ordered crystalline region is reserved, so that the cellulose nanowhiskers with high length-diameter ratio and high purity are separated out; in addition, the used acidic low cosolvent can be recycled, so that the waste acid treatment cost and the environmental pollution risk are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of cellulose nano whiskers, in particular to a cellulose nano whisker and a preparation method thereof, silanized modified cellulose nano whiskers and applications thereof. Background Art

[0002] Nanocellulose whiskers are products obtained by acid hydrolysis of cellulose. They are rod-shaped and have properties such as high Young's modulus and large surface tension. They are widely used in medical materials, ion adsorption and exchange materials, and biofunctional materials.

[0003] Currently, the main methods for preparing cellulose nanowhiskers include acid hydrolysis, bioenzymatic methods, and physical-mechanical methods. Among them, bioenzymatic and physical-mechanical methods are not widely used due to their high cost and the need for special equipment. The acid hydrolysis method uses the infiltrating acid to ionize hydrogen ions, catalytically breaking the glycosidic bonds of the cellulose molecular chain, breaking down the amorphous regions and degrading the cellulose to produce cellulose nanowhiskers. However, the cellulose nanowhiskers prepared by this one-step acid hydrolysis method have uneven particle size, and their aspect ratio and crystallinity are difficult to control, making it difficult to obtain cellulose nanowhiskers with a high aspect ratio and high crystallinity.

[0004] Therefore, how to prepare cellulose nanowhiskers with high aspect ratio and high crystallinity at low cost is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a cellulose nano whisker and a preparation method thereof, a silanized modified cellulose nano whisker and an application thereof. The method provided by the present invention can obtain cellulose nano whiskers with a high aspect ratio and high crystallinity without the need for expensive equipment.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing cellulose nano whiskers, comprising the following steps:

[0008] (1) drying and pulverizing the algae in sequence to obtain algae powder;

[0009] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution and performing an alkali boiling treatment to obtain a suspension;

[0010] (3) mixing the suspension obtained in step (2) with an oxidant solution to perform a bleaching reaction to obtain nanocellulose;

[0011] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent and performing a hydrolysis reaction to obtain cellulose nanowhiskers;

[0012] The acidic low co-solvent consists of a metal salt, a hydrogen bond donor compound, a hydrogen bond acceptor compound, deionized water and an inorganic acid; the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water and the inorganic acid is (0.3-1):(1-3):1:1:(1-2).

[0013] Preferably, the mass concentration of the sodium hydroxide solution in step (2) is 2-6%; and the mass ratio of the algae powder to the sodium hydroxide solution is 1:2-40.

[0014] Preferably, the mass concentration of the oxidant solution in step (3) is 0.5-5%.

[0015] Preferably, the ratio of the mass of the algae powder in step (2) to the mass of the oxidant solution in step (3) is 1:1-15.

[0016] Preferably, the temperature of the bleaching reaction in step (3) is 60-80° C., and the time of the bleaching reaction is 20-80 minutes.

[0017] Preferably, the hydrogen bond donor compound in step (4) includes one or more of urea, glycerol, lactic acid, oxalic acid, citric acid, acetic acid, maleic acid, butyrolactam, caprolactam, guanidine hydrochloride and ammonium thiocyanate; and the hydrogen bond acceptor compound includes one or more of betaine, choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium acetate and trimethyllaurylammonium chloride.

[0018] Preferably, the temperature of the hydrolysis reaction in step (4) is 50-70° C.; and the time of the hydrolysis reaction is 30-60 min.

[0019] The present invention also provides cellulose nano whiskers prepared by the preparation method described in the above technical solution, wherein the diameter of the cellulose nano whiskers is 5 to 50 nm; and the aspect ratio of the cellulose nano whiskers is 800 to 1800.

[0020] The present invention also provides a silanized modified cellulose nanowhiskers, and the preparation method of the silanized modified cellulose nanowhiskers comprises: mixing cellulose nanowhiskers, a silane coupling agent and an ethanol aqueous solution, and performing a coupling reaction to obtain the silanized modified cellulose nanowhiskers; the cellulose nanowhiskers are the cellulose nanowhiskers described in the above technical solution.

[0021] The present invention also provides the use of the silanized modified cellulose nano whiskers in the above technical solution in lithium battery coating diaphragms and food packaging high-barrier diaphragms.

[0022] The present invention provides a method for preparing cellulose nanowhiskers, comprising the following steps: drying and pulverizing algae in sequence to obtain algae powder; mixing the algae powder with a sodium hydroxide solution and performing an alkali boiling treatment to obtain a suspension; mixing the suspension with an oxidant solution and performing a bleaching reaction to obtain nanocellulose; mixing the nanocellulose with an acidic low cosolvent and performing a hydrolysis reaction to obtain cellulose nanowhiskers; the acidic low cosolvent comprises a metal salt, a hydrogen bond donor compound, a hydrogen bond acceptor compound, deionized water, and an inorganic acid; the mass ratio of the metal salt, hydrogen bond donor compound, hydrogen bond acceptor compound, deionized water, and inorganic acid is (0.3-1):(1-3):1:1:(1-2). The present invention uses algae as raw material, which is abundant and inexpensive, and also contains a large amount of cellulose, thereby reducing the cost of preparing cellulose nanowhiskers. The present invention dries and pulverizes algae, resulting in an algae powder with a smaller particle size and a larger contact area with a sodium hydroxide solution. This reduces the amount of sodium hydroxide solution used and reduces costs. It also helps to fully remove impurities from the algae powder, improving the purity and yield of nanocellulose, and thus, the purity and yield of cellulose nanowhiskers. The present invention uses sodium hydroxide solution and algae powder, followed by an alkali digestion treatment, to deeply remove lignin, hemicellulose, and other impurities, thereby obtaining high-purity cellulose fibers and creating the necessary conditions for subsequent acid hydrolysis to separate cellulose nanowhiskers. The present invention also removes residual lignin by mixing the suspension obtained after the alkali digestion with an oxidant solution. It also bleaches the cellulose fibers, improving the purity of the nanocellulose and creating the necessary conditions for subsequent acid hydrolysis to separate cellulose nanowhiskers. The present invention uses an acidic low co-solvent to cause nanocellulose to undergo a hydrolysis reaction. By controlling the composition of the acidic low co-solvent, it can attack the amorphous region in the nanocellulose and hydrolyze it, retaining the highly ordered crystalline region, thereby separating cellulose nanowhiskers with a high aspect ratio and high crystallinity; and the use of an acidic low co-solvent not only avoids the use of highly corrosive and difficult-to-recycle concentrated sulfuric acid, but also allows for recycling, reducing the cost of waste acid treatment and the risk of environmental pollution. In addition, since the cellulose nanowhiskers prepared by the present invention have a high aspect ratio and high purity, after being prepared as a diaphragm, the heat shrinkage resistance is significantly improved, and the moisture content of the diaphragm is effectively reduced. The results of the examples show that the aspect ratio of the cellulose nanowhiskers prepared by the method provided by the present invention can reach more than 1500, and cellulose nanowhiskers with a high aspect ratio and high crystallinity can be prepared, which can greatly improve the wetting tension and oxygen barrier properties of the packaging coating film. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of the cellulose nanowhiskers prepared in Example 1 of the present invention.

[0024] Figure 2 This is a comparison chart of the moisture content of the coated diaphragms of Examples 7 and 8 of the present invention and Comparative Example 4 after drying at 150°C for 24 hours. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing cellulose nano whiskers, comprising the following steps:

[0026] (1) drying and pulverizing the algae in sequence to obtain algae powder;

[0027] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution and performing an alkali boiling treatment to obtain a suspension;

[0028] (3) mixing the suspension obtained in step (2) with an oxidant solution to perform a bleaching reaction to obtain nanocellulose;

[0029] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent and performing a hydrolysis reaction to obtain cellulose nanowhiskers;

[0030] The acidic low co-solvent consists of a metal salt, a hydrogen bond donor compound, a hydrogen bond acceptor compound, deionized water and an inorganic acid; the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water and the inorganic acid is (0.3-1):(1-3):1:1:(1-2).

[0031] The invention sequentially performs drying and pulverizing treatments on algae to obtain algae powder.

[0032] The present invention does not particularly limit the source of the algae, and any algae available to those skilled in the art can be used. In the present invention, the algae are preferably biomass algae from rivers and / or oceans, and more preferably include one or more of Chlorophytum, Spirogyra, Cladophora, Aphanizomenon, Trichoderma, Ulva, Chain Algae, Laminaria, Macrokelp, Sargassum, and Gracilaria. The present invention uses algae as raw materials, which are abundant and inexpensive, and also contain a large amount of cellulose, which can reduce the cost of preparing cellulose nano whiskers and increase the yield of cellulose nano whiskers.

[0033] The present invention preferably removes debris and shellfish attached to the algae before drying. By removing debris and shellfish attached to the algae, the present invention can remove non-cellulose components such as protein and improve the purity of the cellulose nanowhiskers.

[0034] In the present invention, the drying temperature is preferably 60-100°C, more preferably 70-80°C; the drying time is preferably 8-36 hours, more preferably 12-24 hours. The present invention can remove moisture from the algae through drying, making it easier to crush into algae powder.

[0035] The present invention has no particular limitation on the pulverization method. Conventional pulverization methods can be used to reduce the particle size of the algae powder to a desired range.

[0036] In the present invention, the particle size of the algae powder is preferably 10 to 500 μm, more preferably 50 to 300 μm. By controlling the particle size of the algae powder within this range, the present invention can achieve a smaller particle size, providing a larger contact area with the sodium hydroxide solution, thereby reducing the amount of sodium hydroxide solution used and lowering costs. It also helps to fully remove impurities from the algae powder, improving the purity and yield of nanocellulose, and thus increasing the purity and yield of cellulose nanowhiskers.

[0037] After obtaining the algae powder, the present invention mixes the algae powder with a sodium hydroxide solution and performs an alkali boiling treatment to obtain a suspension.

[0038] In the present invention, the mass concentration of the sodium hydroxide solution is preferably 2% to 6%. As an embodiment of the present invention, the mass concentration of the sodium hydroxide solution can be 2%, 3%, 4%, 5% or 6%. The present invention controls the mass concentration of the sodium hydroxide solution within the above range, which is more conducive to fully removing lignin, hemicellulose and other impurities in the algae powder.

[0039] In the present invention, the mass ratio of the algae powder to the sodium hydroxide solution is preferably 1:2 to 40. As one embodiment of the present invention, the mass ratio of the algae powder to the sodium hydroxide solution can be 1:2, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, or 1:40. Controlling the mass ratio of the algae powder to the sodium hydroxide solution within the above range is more conducive to fully removing lignin, hemicellulose, and other impurities from the algae powder.

[0040] The present invention has no particular limitation on the method of mixing the algae powder and the sodium hydroxide solution, and the two can be mixed evenly.

[0041] In the present invention, the temperature of the alkali cooking treatment is preferably 60-120°C. As one embodiment of the present invention, the temperature of the alkali cooking treatment can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C. In the present invention, the duration of the alkali cooking treatment is preferably 80-120 minutes. As one embodiment of the present invention, the duration of the alkali cooking treatment can be 80 minutes, 85 minutes, 90 minutes, 95 minutes, 100 minutes, 105 minutes, 110 minutes, 115 minutes, or 120 minutes. Controlling the temperature and duration of the alkali cooking treatment within the above ranges is more conducive to fully removing lignin, hemicellulose, and other impurities from the algae powder.

[0042] In the present invention, the system after alkali boiling treatment is preferably cooled to room temperature to obtain a suspension.

[0043] After obtaining the suspension, the present invention mixes the suspension with an oxidant solution to perform a bleaching reaction to obtain nanocellulose.

[0044] In the present invention, the mass concentration of the oxidant solution is preferably 0.5-5%. As one embodiment of the present invention, the mass concentration of the oxidant solution can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. By controlling the mass concentration of the oxidant solution within the above range, the present invention can provide good oxidizing properties after mixing with the suspension. In the present invention, the oxidant solution is preferably a sodium hypochlorite solution or a hydrogen peroxide solution.

[0045] In the present invention, when the mass concentration of the oxidant solution is 0.5-5%, the mass ratio of the algae powder to the oxidant solution is preferably 1:1-15. As one embodiment of the present invention, the mass ratio of the algae powder to the oxidant solution can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, or 1:15. By controlling the mass ratio of the algae powder to the oxidant solution within the above range, the present invention can fully remove residual lignin from the suspension after alkali boiling.

[0046] The present invention has no particular limitation on the method for mixing the suspension and the oxidant solution, as long as the two can be mixed evenly.

[0047] In the present invention, the temperature of the bleaching reaction is preferably 60 to 80°C. As an embodiment of the present invention, the temperature of the bleaching reaction can be 60°C, 65°C, 70°C, 75°C, or 80°C. In the present invention, the time of the bleaching reaction is preferably 20 to 80 minutes. As an embodiment of the present invention, the time of the bleaching reaction can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, or 80 minutes. Under the above-mentioned temperature and time, the present invention can use an oxidant to remove residual lignin after alkali boiling, and can also bleach cellulose fibers and improve the purity of nanocellulose.

[0048] The present invention preferably performs solid-liquid separation on the system obtained by the bleaching reaction, and then washes and dries the solid obtained by the solid-liquid separation to obtain nanocellulose. The present invention does not particularly limit the methods of solid-liquid separation, washing, and drying. Conventional solid-liquid separation, washing, and drying methods can be used to fully remove impurities from the nanocellulose and dry it.

[0049] After obtaining the nanocellulose, the present invention mixes the nanocellulose with an acidic low co-solvent and performs a hydrolysis reaction to obtain cellulose nano whiskers.

[0050] In the present invention, the acidic low co-solvent consists of a metal salt, a hydrogen bond donor compound, a hydrogen bond acceptor compound, deionized water and an inorganic acid.

[0051] In the present invention, the metal salt preferably includes one or more of aluminum chloride, ferric chloride, zinc chloride and lithium chloride. The metal salt used in the present invention can reduce the viscosity of the acidic low co-solvent system and improve mass transfer efficiency.

[0052] In the present invention, the hydrogen bond donor compound preferably includes one or more of urea, glycerol, lactic acid, oxalic acid, citric acid, acetic acid, maleic acid, butyrolactam, caprolactam, guanidine hydrochloride, and ammonium thiocyanate. These hydrogen bond donor compounds can donate protons, creating an acidic environment; participate in the formation of a eutectic network, lowering the melting point of the system and enabling room-temperature liquid operation; and disrupt the cellulose hydrogen bond network, forming hydrogen bonds with cellulose hydroxyl groups, swelling the fiber structure, and exposing amorphous regions.

[0053] In the present invention, the hydrogen bond acceptor compound preferably includes one or more of betaine, choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium acetate, and trimethyllaurylammonium chloride. The hydrogen bond acceptor compound utilized in the present invention can disrupt the ion / hydrogen bond network, lower the melting point, and promote the dissolution and penetration of cellulose.

[0054] In the present invention, the inorganic acid preferably includes one or more of sulfuric acid, hydrochloric acid, nitric acid, acetic acid and phosphoric acid. The present invention can enhance the acidity, accelerate the hydrolysis kinetics, and enhance the H + The electrophilicity of the reaction mixture improves the efficiency of glycosidic bond cleavage, limits the decomposition of organic acids, and ensures uniform and stable reactions. In an embodiment of the present invention, the mass concentration of the sulfuric acid can be 54%; the mass concentration of the hydrochloric acid can be 15-18%; the mass concentration of the nitric acid can be 30%; the mass concentration of the acetic acid can be 99%; and the mass concentration of the phosphoric acid can be 85%.

[0055] In the present invention, the mass ratio of the metal salt, hydrogen bond donor compound, hydrogen bond acceptor compound, deionized water, and inorganic acid is (0.3-1):(1-3):1:1:(1-2), preferably (0.5-0.8):(1-2):1:1:(1.5-2). By controlling the mass ratio of the metal salt, hydrogen bond donor compound, hydrogen bond acceptor compound, deionized water, and inorganic acid within the above range, the present invention can attack and hydrolyze the amorphous regions in the nanocellulose, retaining the highly ordered crystalline regions, thereby separating cellulose nanowhiskers with a high aspect ratio and high crystallinity.

[0056] In the present invention, the ratio of the mass of the nanocellulose to the mass of the acidic low co-solvent is preferably 1:5 to 50. As one embodiment of the present invention, the ratio of the mass of the nanocellulose to the mass of the acidic low co-solvent can be 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, or 1:40. Controlling the ratio of the mass of the nanocellulose to the mass of the acidic low co-solvent within the above range is more conducive to fully hydrolyzing the nanocellulose to form cellulose nanowhiskers.

[0057] The present invention has no particular limitation on the method for mixing the nanocellulose and the acidic low co-solvent. Conventional mixing methods can be used as long as the two are evenly mixed.

[0058] In the present invention, the temperature of the hydrolysis reaction is preferably 50 to 70°C. As an embodiment of the present invention, the temperature of the hydrolysis reaction may be 50°C, 55°C, 60°C, 65°C or 70°C. In the present invention, the time of the hydrolysis reaction is preferably 30 to 60 minutes. As an embodiment of the present invention, the time of the hydrolysis reaction may be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes. The present invention carries out the hydrolysis reaction at the above-mentioned temperature and time, which is more conducive to fully dissolving the amorphous regions in the nanocellulose and retaining the highly ordered crystalline regions, thereby separating cellulose nanowhiskers with a high aspect ratio and high crystallinity.

[0059] The present invention also provides cellulose nano whiskers prepared by the preparation method described in the above technical solution.

[0060] In the present invention, the diameter of the cellulose nanowhiskers is 5 to 50 nm, preferably 10 to 40 nm. In the present invention, the aspect ratio of the cellulose nanowhiskers is 800 to 1800, preferably 1000 to 1500.

[0061] The method provided by the present invention uses algae as raw materials, and can remove impurities such as lignin through alkali boiling treatment and bleaching reaction to obtain high-purity, high-aspect ratio nanocellulose; an acidic low co-solvent is used to cause a hydrolysis reaction in the nanocellulose. By controlling the composition of the acidic low co-solvent, the amorphous regions in the nanocellulose can be precisely attacked and hydrolyzed, retaining highly ordered crystalline regions, thereby separating cellulose nanowhiskers with a high aspect ratio and high crystallinity.

[0062] The present invention also provides a silanized modified cellulose nano whisker. The preparation method of the silanized modified cellulose nano whisker comprises: mixing cellulose nano whiskers, a silane coupling agent and an ethanol aqueous solution, and performing a coupling reaction to obtain the silanized modified cellulose nano whisker.

[0063] In the present invention, the cellulose nano whiskers are the cellulose nano whiskers described in the above technical solution.

[0064] In the present invention, the silane coupling agent preferably includes one or more of γ-mercaptopropyltrimethoxysilane KH-590, γ-mercaptopropyltriethoxysilane KH-580, mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltributoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, silane coupling agent Si-40, diethylenetriaminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, and n-octyltriethoxysilane. By using the above silane coupling agents, the present invention can modify cellulose nanowhiskers and improve the hydrophobicity of the cellulose nanowhiskers.

[0065] In the present invention, the mass ratio of the cellulose nanowhiskers, silane coupling agent, and ethanol aqueous solution is preferably 1:(0.5-3):(5-30), and more preferably 1:(1-2):(10-20). By controlling the mass ratio of the cellulose nanowhiskers, silane coupling agent, and ethanol aqueous solution within the above range, the present invention can fully modify the cellulose nanowhiskers, improving their hydrophobicity and dispersibility in non-polar solvents.

[0066] In the present invention, the mass ratio of ethanol to deionized water in the ethanol aqueous solution is preferably (7-9):(1-3), more preferably (8-9):(2-3). The present invention uses ethanol aqueous solution as the reaction solvent to promote the coupling reaction.

[0067] In the present invention, the temperature of the coupling reaction is preferably 40 to 60°C. As an embodiment of the present invention, the temperature of the coupling reaction can be 40°C, 45°C, 50°C, 55°C or 60°C. In the present invention, the time of the coupling reaction is preferably 30 to 60 minutes. As an embodiment of the present invention, the time of the coupling reaction can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes. The present invention, at the above temperature and time, can promote the sufficient coupling modification of cellulose nanowhiskers.

[0068] The present invention preferably filters, washes, and dries the coupling reaction system to obtain silanized modified cellulose nanowhiskers. The present invention does not particularly limit the methods of filtering, washing, and drying. Conventional filtering, washing, and drying methods can be used to fully remove impurities in the silanized modified cellulose nanowhiskers.

[0069] The present invention also provides the use of the silanized modified cellulose nano whiskers described in the above technical solution in lithium battery coating diaphragms or food packaging high-barrier diaphragms.

[0070] The present invention has no special limitation on the method of applying the silanized modified cellulose nano whiskers in the lithium battery coating diaphragm and the food packaging high-barrier diaphragm, and any conventional application method can be used.

[0071] The silanized modified cellulose nanowhiskers provided by the present invention have a high aspect ratio and are modified by silane coupling, which can reduce the polarity of the cellulose nanowhiskers, enhance their compatibility with the polymer matrix, have good hydrophobic properties, and improve their dispersibility in non-polar solvents, and can be used for lithium battery coating diaphragms and high-barrier diaphragms for food packaging.

[0072] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0073] Example 1

[0074] A method for preparing cellulose nano whiskers, comprising the following steps:

[0075] (1) After removing debris and shellfish attached to algae (Cladophora), the algae were dried at 80°C for 24 hours and crushed to obtain algae powder with a particle size of 100 μm;

[0076] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:20, performing an alkali boiling treatment at 60° C. for 120 minutes, and cooling to room temperature to obtain a suspension;

[0077] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 5% in a mass ratio of 1:10, performing a bleaching reaction at 60° C. for 60 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0078] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent in a mass ratio of 1:30, performing a hydrolysis reaction at 60° C. for 30 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0079] The acidic low co-solvent is composed of a metal salt (lithium chloride), a hydrogen bond donor compound (citric acid), a hydrogen bond acceptor compound (choline chloride), deionized water, and an inorganic acid (18% hydrochloric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.3:3:1:1:1;

[0080] The SEM images of the cellulose nanowhiskers prepared in this example are as follows: Figure 1 As shown. Figure 1 It can be seen that the cellulose nanowhiskers prepared by the method provided by the present invention have a nanometer-scale diameter and a high aspect ratio.

[0081] According to tests, the average diameter of the cellulose nano whiskers prepared in this embodiment is 15 nm, the aspect ratio is 1700, and the purity of the cellulose nano whiskers is 97.2%.

[0082] Example 2

[0083] A method for preparing cellulose nano whiskers, comprising the following steps:

[0084] (1) After removing debris and shellfish attached to the algae (Aplastrum fasciatum), the algae were dried at 80°C for 24 hours and crushed to obtain algae powder with a particle size of 110 μm;

[0085] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 4% in a mass ratio of 1:15, performing alkali boiling treatment at 80° C. for 120 minutes, and cooling to room temperature to obtain a suspension;

[0086] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 4.5% in a mass ratio of 1:15, performing a bleaching reaction at 75° C. for 75 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0087] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent in a mass ratio of 1:35, performing a hydrolysis reaction at 65° C. for 45 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0088] The acidic low co-solvent is composed of a metal salt (ferric chloride), a hydrogen bond donor compound (urea), a hydrogen bond acceptor compound (tetrabutylammonium chloride), deionized water, and an inorganic acid (85% phosphoric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.5:2:1:1:1.5;

[0089] According to tests, the average diameter of the cellulose nano whiskers prepared in this embodiment is 22 nm, the aspect ratio is 1620, and the purity of the cellulose nano whiskers is 82.5%.

[0090] Example 3

[0091] A method for preparing cellulose nano whiskers, comprising the following steps:

[0092] (1) After removing debris and shellfish attached to algae (macroalgae), the algae were dried at 70°C for 24 hours and crushed to obtain algae powder with a particle size of (15 μm);

[0093] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 4% in a mass ratio of 1:30, performing an alkali boiling treatment at 80° C. for 100 minutes, and cooling to room temperature to obtain a suspension;

[0094] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 3% in a mass ratio of 1:10, performing a bleaching reaction at 60° C. for 60 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0095] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent in a mass ratio of 1:15, performing a hydrolysis reaction at 55° C. for 45 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0096] The acidic low co-solvent is composed of a metal salt (aluminum chloride), a hydrogen bond donor compound (lactic acid), a hydrogen bond acceptor compound (trimethyl lauryl ammonium chloride), deionized water, and an inorganic acid (54% sulfuric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.7:2.5:1:1:1.5;

[0097] According to tests, the average diameter of the cellulose nanowhiskers prepared in this embodiment is 21 nm, the aspect ratio is 1600, and the purity of the cellulose nanowhiskers is 78.3%.

[0098] Example 4

[0099] A method for preparing cellulose nano whiskers, comprising the following steps:

[0100] (1) After removing debris and shellfish attached to the algae (Caudata), the algae were dried at 80°C for 24 hours and crushed to obtain algae powder with a particle size of 105 μm;

[0101] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:30, performing an alkali boiling treatment at 100° C. for 100 minutes, and cooling to room temperature to obtain a suspension;

[0102] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 2% in a mass ratio of 1:10, performing a bleaching reaction at 75° C. for 50 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0103] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent in a mass ratio of 1:35, performing a hydrolysis reaction at 55° C. for 45 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0104] The acidic low co-solvent is composed of a metal salt (zinc chloride), a hydrogen bond donor compound (guanidine hydrochloride), a hydrogen bond acceptor compound (choline chloride), deionized water, and an inorganic acid (30% nitric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.8:2.5:1:1:1;

[0105] According to tests, the average diameter of the cellulose nano whiskers prepared in this embodiment is 25 μm, the aspect ratio is 1500, and the purity of the cellulose nano whiskers is 78.3%.

[0106] Example 5

[0107] A method for preparing cellulose nano whiskers, comprising the following steps:

[0108] (1) After removing debris and shellfish attached to the algae (Streptomyces fasciatus), the algae were dried at 80°C for 24 hours and crushed to obtain algae powder with a particle size of 98 μm;

[0109] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 2% in a mass ratio of 1:40, performing an alkali boiling treatment at 120° C. for 120 minutes, and cooling to room temperature to obtain a suspension;

[0110] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 4% in a mass ratio of 1:15, performing a bleaching reaction at 60° C. for 60 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0111] (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent in a mass ratio of 1:15, performing a hydrolysis reaction at 60° C. for 50 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0112] The acidic low co-solvent is composed of a metal salt (lithium chloride), a hydrogen bond donor compound (acetic acid), a hydrogen bond acceptor compound (tetramethylammonium chloride), deionized water, and an inorganic acid (15% hydrochloric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.3:2:1:1:1;

[0113] According to tests, the average diameter of the cellulose nano whiskers prepared in this embodiment is 26 nm, the aspect ratio is 1580, and the purity of the cellulose nano whiskers is 58.3%.

[0114] Comparative Example 1

[0115] A method for preparing cellulose nano whiskers, comprising the following steps:

[0116] (1) After removing debris and shellfish attached to the algae (Gracilaria lemaneiformis), the algae were dried at 80°C for 24 hours and crushed to obtain algae powder with a particle size of 160 μm;

[0117] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 5% in a mass ratio of 1:20, performing an alkali boiling treatment at 60° C. for 120 minutes, and cooling to room temperature to obtain a suspension;

[0118] (3) mixing the suspension obtained in step (2) with a sodium hypochlorite solution having a mass concentration of 5% in a mass ratio of 1:10, performing a bleaching reaction at 60° C. for 60 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0119] (4) mixing the nanocellulose obtained in step (3) with 5% hydrochloric acid in a mass ratio of 1:20, performing a hydrolysis reaction at 70° C. for 60 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0120] According to tests, the diameter of the cellulose nano whiskers prepared in this embodiment is 25 nm, the aspect ratio is 580, and the purity of the cellulose nano whiskers is 83.2%.

[0121] Comparative Example 2

[0122] A method for preparing cellulose nano whiskers, comprising the following steps:

[0123] (1) The plant (bamboo) was dried at 100°C for 30 hours and then crushed to obtain plant powder with a particle size of 300 μm;

[0124] (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution having a mass concentration of 4% in a mass ratio of 1:40, performing an alkali boiling treatment at 100° C. for 120 minutes, and cooling to room temperature to obtain a suspension;

[0125] (3) mixing the nanocellulose obtained in step (2) with an acidic low co-solvent in a mass ratio of 1:15, performing a hydrolysis reaction at 50° C. for 30 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0126] The acidic low co-solvent is composed of a metal salt (lithium chloride), a hydrogen bond donor compound (maleic acid), a hydrogen bond acceptor compound (choline chloride), deionized water, and an inorganic acid (phosphoric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.3:3:1:1:1;

[0127] According to tests, the diameter of the cellulose nano whiskers prepared in this embodiment is 20, the aspect ratio is 700, and the purity of the cellulose nano whiskers is 62.8%.

[0128] Comparative Example 3

[0129] A method for preparing cellulose nano whiskers, comprising the following steps:

[0130] (1) After removing debris and shellfish attached to the algae (Trichoderma), the algae were dried at 80°C for 24 hours and then crushed to obtain algae powder with a particle size of 120 μm;

[0131] (2) mixing the algae powder obtained in step (1) with a sodium hypochlorite solution having a mass concentration of 5% in a mass ratio of 1:10, performing a bleaching reaction at 75° C. for 60 minutes, filtering, washing and drying the obtained solid to obtain nanocellulose;

[0132] (3) mixing the nanocellulose obtained in step (2) with an acidic low co-solvent in a mass ratio of 1:20, performing a hydrolysis reaction at 55° C. for 45 minutes, and then filtering, washing and drying to obtain cellulose nanowhiskers;

[0133] The acidic low co-solvent is composed of a metal salt (lithium chloride), a hydrogen bond donor compound (citric acid), a hydrogen bond acceptor compound (choline chloride), deionized water, and an inorganic acid (hydrochloric acid); the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water, and the inorganic acid is 0.3:3:1:1:1;

[0134] According to tests, the diameter of the cellulose nano whiskers prepared in this embodiment is 17 nm, the aspect ratio is 820, and the purity of the cellulose nano whiskers is 42.3%.

[0135] Example 6

[0136] A silanized modified cellulose nanowhiskers is prepared by a method comprising: mixing the cellulose nanowhiskers prepared in Example 1, a silane coupling agent (mercaptopropylmethyldimethoxysilane), and an ethanol aqueous solution (the mass ratio of ethanol to deionized water is 7:3) in a mass ratio of 1:2:25, carrying out a coupling reaction at 60°C for 50 minutes, filtering, washing, and drying to obtain the silanized modified cellulose nanowhiskers.

[0137] Example 7

[0138] A nanofiber coating liquid and a lithium-ion battery coating diaphragm, comprising, by weight, 40 parts of large-particle ceramic powder (porous alumina, D50 of 0.4 μm, pore size of 20 nm), 45 parts of small-particle inorganic powder (fumed alumina, D50 of 45 nm), 10 parts of cellulose nanowhiskers prepared in Example 1, 5 parts of a polyacrylic acid binder, and 500 parts of water; the nanofiber coating liquid has a solid content of 20%; and the lithium-ion battery coating diaphragm is obtained by coating the coating liquid on one or both sides of a polyolefin base film.

[0139] The preparation method of the nanofiber coating liquid comprises the following steps: dispersing large-particle ceramic powder, small-particle inorganic powder and cellulose nano whiskers in a polar solvent to obtain a dispersion liquid; mixing the dispersion liquid with a binder, and filtering the mixture through a 500-mesh filter to obtain the nanofiber coating liquid.

[0140] Example 8

[0141] A silanized modified nanofiber coating liquid and a lithium-ion battery coating diaphragm, comprising, by weight, 40 parts of large-particle ceramic powder (porous alumina, D50 of 0.4 μm, pore size of 20 nm), 45 parts of small-particle inorganic powder (fumed alumina, D50 of 45 nm), 10 parts of silanized modified cellulose nanowhiskers prepared in Example 6, 5 parts of a polyacrylic acid binder, and 500 parts of water; the modified nanofiber coating liquid has a solid content of 20%; and the lithium-ion battery coating diaphragm is obtained by coating the coating liquid on one or both sides of a polyolefin base film.

[0142] The preparation method of the silanized modified nanofiber coating liquid is consistent with that of Example 7.

[0143] Example 9

[0144] A nanofiber coating liquid and a high-barrier diaphragm for food packaging, comprising, by weight, 9 parts of cellulose nanowhiskers prepared in Example 1, 1 part of a polyvinyl alcohol binder, and 100 parts of water; the modified nanofiber coating liquid has a solid content of 9%. The high-barrier diaphragm for food packaging can be obtained by coating the coating liquid on one or both sides of a base film (such as BOPP, PLA, PA, or CPP).

[0145] The preparation method of the nanofiber coating liquid comprises the following steps: dispersing the nanofibers in a polar solvent to obtain a dispersion liquid; mixing the dispersion liquid with a binder, and filtering the mixture through a 500-mesh filter to obtain the nanofiber coating liquid.

[0146] Example 10

[0147] A silanized modified nanofiber coating liquid and a high-barrier diaphragm for food packaging, comprising, by weight, 9 parts of silanized modified cellulose nanowhiskers prepared in Example 6, 1 part of a polyvinyl alcohol binder, and 100 parts of water; the modified nanofiber coating liquid has a solid content of 9%. The high-barrier diaphragm for food packaging can be obtained by coating the coating liquid on one or both sides of a base film (such as BOPP, PLA, PA, or CPP).

[0148] The preparation method of the silanized modified nanofiber coating liquid is consistent with that of Example 9.

[0149] Comparative Example 4

[0150] Disclosed are an alumina coating liquid and a lithium-ion battery coating diaphragm. The components, measured by weight, are: 45 parts of large-particle ceramic powder (porous alumina, D50 is 0.4 μm, pore size is 20 nm), 50 parts of small-particle inorganic powder (fumed alumina, D50 is 45 nm), 5 parts of a polyacrylic acid binder, and 500 parts of water. The modified nanofiber coating liquid has a solid content of 20%. The lithium-ion battery coating diaphragm can be obtained by coating the coating liquid on one or both sides of a polyolefin base film.

[0151] The preparation method of the aluminum oxide coating liquid is consistent with that of Example 7.

[0152] Comparative Example 5

[0153] An ethylene-vinyl alcohol copolymer (EVOH) coating liquid and a high-barrier diaphragm for food packaging, comprising, by weight, 9 parts of ethylene-vinyl alcohol copolymer, 1 part of a polyvinyl alcohol binder, and 100 parts of water; the ethylene-vinyl alcohol copolymer (EVOH) coating liquid has a solid content of 9%. The high-barrier diaphragm for food packaging can be obtained by coating the coating liquid on both sides of a BOPP base film.

[0154] The preparation method of the ethylene-vinyl alcohol copolymer (EVOH) coating liquid is the same as that of Example 9.

[0155] The performance of Examples 7 and 8 was tested against Comparative Example 4 and the base film, and the results are shown in Table 1; the performance test results of Examples 9 and 10 against the base film are shown in Table 2.

[0156] Among them, a thickness tester is used to measure the thickness of the battery separator, and 5 points are randomly taken on the separator for measurement to calculate the average value; the thermal shrinkage test is carried out according to the method in GB / T12027-2004; the oxygen permeability test is carried out according to the method in GB / T1038.1-2022; the haze (Fog) test is carried out according to the method in GB / T2410-2008; the dynamic friction coefficient test is carried out according to the method in GB / T 10006-1998; the wetting tension test is carried out according to the method in GB / T 14216-2008; for the moisture content test, the coated separator is dried in a blast drying oven, placed in a water-free and oxygen-free glove box for drying for 24 hours, and finally tested in a Karl Fischer titrator at a heating rate of 5°C per minute and 150°C.

[0157] Table 1 Performance test results of Examples 7 and 8 compared with Comparative Example 4 and base film

[0158]

[0159]

[0160] Table 2 Performance test results of Examples 9 and 10 compared with Comparative Example 5 and base film

[0161]

[0162] The comparison of moisture content of the coated diaphragms of Examples 7 and 8 of the present invention and Comparative Example 4 after drying at 150°C for 24 hours is shown in the figure below. Figure 2 shown.

[0163] The above results show that the aspect ratio and purity of the cellulose nanowhiskers prepared by the method provided by the present invention are significantly higher than those of the comparative example, demonstrating that the method provided by the present invention can produce cellulose nanowhiskers with a high aspect ratio and purity. This is because the present invention selects algae as the raw material and removes lignin, hemicellulose, and other impurities through alkali boiling and bleaching, thereby obtaining high-purity, high-aspect-ratio cellulose fibers. Then, an acidic low co-solvent is used to hydrolyze the nanocellulose. By controlling the composition of the acidic low co-solvent, the amorphous regions in the nanocellulose are precisely targeted and hydrolyzed, retaining the highly ordered crystalline regions, thereby separating cellulose nanowhiskers with a high aspect ratio and high purity. Furthermore, due to the high aspect ratio and high purity of the cellulose nanowhiskers prepared by the present invention, after being prepared into a separator, the heat shrinkage resistance is significantly improved and the moisture content of the separator is effectively reduced. Furthermore, the application of the prepared cellulose nanowhiskers and silanized cellulose nanowhiskers in food packaging film coatings can significantly improve the wetting tension and oxygen barrier properties of the food packaging coating film.

[0164] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing cellulose nano whiskers, comprising the following steps: (1) drying and pulverizing the algae in sequence to obtain algae powder; (2) mixing the algae powder obtained in step (1) with a sodium hydroxide solution and performing an alkali boiling treatment to obtain a suspension; (3) mixing the suspension obtained in step (2) with an oxidant solution to perform a bleaching reaction to obtain nanocellulose; (4) mixing the nanocellulose obtained in step (3) with an acidic low co-solvent and performing a hydrolysis reaction to obtain cellulose nanowhiskers; The acidic low co-solvent consists of a metal salt, a hydrogen bond donor compound, a hydrogen bond acceptor compound, deionized water and an inorganic acid; the mass ratio of the metal salt, the hydrogen bond donor compound, the hydrogen bond acceptor compound, the deionized water and the inorganic acid is (0.3-1):(1-3):1:1:(1-2).

2. The preparation method according to claim 1, characterized in that The mass concentration of the sodium hydroxide solution in step (2) is 2-6%; the mass ratio of the algae plant powder to the sodium hydroxide solution is 1:2-40.

3. The preparation method according to claim 1, characterized in that The mass concentration of the oxidant solution in step (3) is 0.5-5%.

4. The preparation method according to claim 1 or 3, characterized in that The mass ratio of the algae powder in step (2) to the mass ratio of the oxidant solution in step (3) is 1:1-15.

5. The preparation method according to claim 1, characterized in that The temperature of the bleaching reaction in step (3) is 60-80° C.; and the time of the bleaching reaction is 20-80 minutes.

6. The preparation method according to claim 1, characterized in that The hydrogen bond donor compound in step (4) includes one or more of urea, glycerol, lactic acid, oxalic acid, citric acid, acetic acid, maleic acid, butyrolactam, caprolactam, guanidine hydrochloride and ammonium thiocyanate; the hydrogen bond acceptor compound includes one or more of betaine, choline chloride, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium acetate and trimethyllaurylammonium chloride.

7. The preparation method according to claim 1, characterized in that The temperature of the hydrolysis reaction in step (4) is 50-70° C.; the time of the hydrolysis reaction is 30-60 minutes.

8. The cellulose nanowhiskers prepared by the preparation method according to any one of claims 1 to 7, wherein the diameter of the cellulose nanowhiskers is 5 to 50 nm; and the aspect ratio of the cellulose nanowhiskers is 800 to 1800.

9. A silanized modified cellulose nanowhiskers, wherein the preparation method of the silanized modified cellulose nanowhiskers comprises: mixing cellulose nanowhiskers, a silane coupling agent and an ethanol aqueous solution to carry out a coupling reaction to obtain silanized modified cellulose nanowhiskers; The cellulose nanowhiskers are the cellulose nanowhiskers according to claim 8.

10. Use of the silanized modified cellulose nanowhiskers according to claim 9 in lithium battery coating diaphragms or food packaging barrier films.

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